The second and third partitions of Poland occur during the reign of Frederick the Great's nephew and successor, Frederick William II. Far less decisive than his uncle, he plays a relatively feeble role in the first response of Europe's crowned heads to the republican threat from France.

He is persuaded to join Austria in the invasion of France in 1792, but energetic French retaliation (combined with his greater interest in winning a good share of Poland) prompts him to sign a separate treaty with France in Basel in 1795 - beginning ten years in which Prussia stands on the sideline of Europe's great conflict. The same policy is followed by his son, Frederick William III, who succeeds him in 1797.

Napoleon against Russia and Prussia: 1806-1807

Until 1806 Prussia maintains a nervous neutrality during the warfare between its powerful neighbours. But the Confederation of the Rhine, organized by Napoleon in July of this year, seems to threaten Prussian interests. In September Frederick William III joins Russia against Napoleon.

The result is rapid disaster. Once again Napoleon moves quickly enough to destroy one of his opponents before the other can arrive in support. Two Prussian armies are engaged on the same day, 14 October 1806, at Jena and Auerstadt - about thirteen miles apart.

At both sites the French are victorious. Within six weeks, before Russian assistance arrives, Napoleon overruns the whole of Prussia.

The Russians prove, at first, rather tougher opponents. A two-day engagement at Eylau (7-8 February 1807) brings heavy casualties but no advantage to either side. But at Friedland, on June 14, Napoleon wins a decisive victory over the Russian army. The result is the extraordinary meeting between Napoleon and the Russian tsar, Alexander I, on 25 June 1807 near Tilsit. Neither will set foot on territory held by the other, so it is agreed that they will meet in the middle of the river, the Neman, which forms the border between them.

An elegant room is built on a raft with a door on either side, each showing the appropriate imperial eagle. The two emperors cast off from their respective river banks at the same moment, but the French oarsmen outrow the Russians. Napoleon is far enough ahead to be able to open the Russian door from the inside and greet the tsar.

The two men get on well. Together they set about carving up Europe. After two weeks of conference Russia's ally Prussia has been gravely weakened, by mutual agreement between the emperors. Russia could easily have fought on after Friedland. But Prussia is occupied by the French and is helpless.

Prussia's share of Poland is now taken to provide the grand duchy of Warsaw, to be ruled by the king of Saxony (a newly acquired ally of Napoleon). And Prussian territory is severely shaved in the west to make room for a kingdom of Westphalia. French troops will remain in Prussia until an indemnity of 120 million francs has been paid. And Prussia is to close her ports to Britain as part of Napoleon's new Continental System.

This painful result keeps Prussia in a cowed state for several years. Like Austria, she sends troops against Russia in Napoleon's campaign of 1812. But the damage done to Napoleon that winter finally gives Frederick William III the courage to send Prussia into war against France for the third time.

On the winning side: 1813-1815

Prussia's declaration of war, in March 1813, brings out of retirement a grand old man of the Prussian army, Gebhard von Blücher. He is already seventy-one when he rejoins the colours. The next two years bring him great distinction.

After campaigning successfully during the summer of 1813, he commands the Prussian army in the great victory at Leipzig in October. He crosses the Rhine on 1 January 1814 and fights his way alongside the Austrians towards Paris, which is captured at the end of March. Napoleon's first abdication sends Blücher back into retirement, from which he emerges for one last triumph. Beaten by Napoleon at Ligny in 1815, he has his revenge two days later at Waterloo.

After an otherwise dismal war, the events of these last two years confirm Prussia's status as one of the four great powers (Austria, Russia, Prussia, Britain) who have together toppled Napoleon. This gives the kingdom a proper status in the Congress of Vienna, where the king is represented by his chancellor, prince von Hardenberg.

Hardenberg's hardline stance in the diplomatic struggle for Polish and Saxon territory pushes the negotiations to the brink of war, but in the end a compromise is reached. It brings Prussia new land in the west, up to and beyond the Rhine, and firmly re-establishes the kingdom as the greatest power of northern Germany - ready now to contest with Austria the leadership of all the German states.

Deutscher Bund and Zollverein: 1815-1834

The congress of Vienna puts in place a revised version of the Confederation of the Rhine. The German states, much reduced in number as a result of Napoleon's interference, now consist of thirty-five monarchies of various kinds and four free cities (Hamburg, Bremen, Lübeck and Frankfurt).

They are organized from 1815 into a Deutscher Bund or German Confederation. It is a body with no legislative powers, being merely a diplomatic assembly of rulers or their representatives. Some of the members have only a subsidiary interest in Germany. The British king has a place, as king of Hanover. So does his Danish counterpart, as duke of Holstein.

The assembly meets in Frankfurt and is known as the Bundestag, in succession to the Reichstag of the now defunct Holy Roman empire. Just as the Habsburg emperor presided over the Reichstag, so the Austrian representative is president of this new institution. Its very existence derives from the efforts of Metternich, determined to continue in this new form the hegemony of Austria among the German nations.

By its nature the Confederation can achieve little in the way of change, since it has no authority over individual members except in foreign policy. But it has, as Metternich would wish, a calming effect - or a stultifying one, depending on the point of view.

Good relations within the Confederation depend on an understanding between the two most powerful members, Austria and Prussia, and here the long survival of a trio of colleagues from the congress of Vienna proves a significant factor. The Austrian emperor Francis I lives until 1835; Frederick William III of Prussia dies in 1840; Metternich remains chancellor of Austria until 1848.

All three are equally reluctant to see political change or to introduce liberal measures. Frederick William promises in 1815 a Prussian constitution, but takes no step towards providing one in the next quarter century. However, on the economic front he introduces reforms of profound significance.

The congress of Vienna has given Prussia extensive new lands around the Rhine and the Moselle (partly to protect the new kingdom of the Netherlands from French aggression), but these regions are isolated from the rest of Prussia, being separated by Hanover and other smaller states.

In an effort to bind together his extended kingdom, Frederick William in 1818 turns all his territories into a single customs-free zone. The benefit to trade encourages neighbouring regions to join this Zollverein (customs union), until by 1834 it covers almost the whole of Germany. Austria, with economic links far beyond the German area, is deliberately excluded. So Prussia, as if by the back door, acquires a role of German leadership.

Revolutions and the Frankfurt assembly: 1848

The immediate effect of the revolutions which sweep through Europe in 1848 is concession on the part of terrified rulers. Riots in Munich cause the king of Bavaria, Louis I, to abdicate in favour of his son. Unrest in Vienna is rapidly followed by the resignation of the veteran chancellor Metternich. Two days of street fighting in Berlin prompt the king of Prussia, now Frederick William IV, to propose a national assembly which will consider a German constitution.

As a result of this promise, elections are rapidly held in the various German states (in many of them by universal male suffrage). On 18 May 1848 some 600 delegates gather in Frankfurt.

Each delegate hopes to find a way of achieving a united and constitutional Germany. But there are strongly differing views as to how this might be realized.

Bavaria, as leader of the middling and smaller states, campaigns for some tripartite arrangement in which their group would hold the balance between Prussia and Austria. Protestants supporting Prussia argue for a kleindeutsch ('small German') solution which excludes Austria. Catholics prefer the grossdeutsch way, to include at least the German-speaking parts of the Austrian empire.

The grossdeutsch cause is severely damaged early in March 1849 when Austria introduces a new constitution treating her entire empire (including Hungary and north Italy) as a single unitary state.

Clearly this is incompatible with a united Germany. On March 28 the delegates at Frankfurt take the kleindeutsch route; they elect the Prussian king, Frederick William IV, as emperor of the Germans. A deputation sets off to Berlin to offer him the crown, but on April 3 he turns it down. The official reason is that only his fellow princes can do him this honour. The harsher truth is that he no longer needs to ally himself with these elected liberals. The tide of reaction has already turned.

In both Berlin and Vienna authoritarian governments are back in position by the spring of 1849. The hard work of avoiding change can be resumed.

But the underlying contest between Prussia and Austria for leadership of the German states remains the most important issue confronting the region. It will eventually be resolved as the result of a crisis which also flares up for the first time in the late 1840s - the question of Schleswig-Holstein.

Schleswig-Holstein: 1848-1864

The region of Schleswig-Holstein, at the interface between German and Danish-speaking regions but with no clear geographical boundaries, is a natural place for conflict in an era of growing nationalism. Historically Holstein has been within the German empire and Schleswig outside it, but both duchies have been attached to the Danish crown since 1460.

In the excitement of 1848 a revolutionary group seizes Kiel, declares the independence of the two duchies from Denmark and appeals to the German Confederation for help. The result is an invasion of Schleswig-Holstein, and then of Denmark itself, by a Prussian army on behalf of the Confederation.

On this occasion international pressure forces the Prussians to withdraw and the two duchies are restored to Denmark. But the crisis flares again in 1863 when the Danish king Frederick VII dies. He has no direct male heir. In Denmark the crown can pass through the female line; but Holstein, like the rest of the German empire, observes the Salic law.

This casts doubt on the right of the new Danish king, Christian IX, to the duchy of Holstein. The German Confederation (still officially presided over by Austria) decides to act. A joint Austrian and Prussian army overruns both Holstein and Schleswig. The result this time is that the two duchies are ceded jointly to Prussia and Austria, by the treaty of Vienna in October 1864.

At the best of times agreement on how to administer the new territories would be difficult to achieve between Prussia and Austria, as rivals for hegemony in Germany. It is made more so now by the fact that Prussia has an agressive and skilful new prime minister, Otto von Bismarck, appointed by William I in 1862. He is determined that Prussia shall replace Austria as leader of the German states, and he sees his chance in Schleswig-Holstein.

It is agreed in 1865 that Prussia will administer Schleswig while Austria will be responsible for Holstein. In June 1866 Bismarck contrives to find fault with Austria's part of the bargain. Prussian troops march from Schleswig into Holstein.

Austria, presiding over the German Confederation (a role acquired half a century earlier at the congress of Vienna), proposes that the Confederation as a whole should restrain its belligerent member. Prussia, certain to be outvoted on the issue, responds on 14 June 1866 by declaring the Confederation defunct.

On June 15, when Saxony, Hanover and Hesse-Kassel refuse to give assurances that they will remain neutral, Prussia invades all three states. The war deciding the future shape of Germany has begun. It will be a short one.

Seven Weeks' War: 1866

The speed of Prussia's victory in the war of 1866 against Austria is largely the result of reforms carried out in the Prussian army by Helmut von Moltke. Appointed chief of the general staff in 1857, he appreciates that recent technological developments - in particular railways and telegraphy - transform the nature of war (as the civil war in America has recently shown). Troops can move fast to seize sudden opportunities. Separate armies can remain in communication while fighting a single campaign on an extended front.

This new strategy requires a much larger and more highly trained general staff, responsible for overall planning and the provision of accurate maps and up-to-date intelligence.

Moltke has several years in which to train his staff and develop new battle plans before Prussia has to face an enemy of equal stature - the Austrian empire, in 1866. He also has the advantage that the Prussian army is now fully equipped with the Dreyse breech-loading rifle (introduced from 1848). The Austrian infantry, still loading their muskets by ramming powder and shot down the muzzle, have a much slower rate of fire.

With these advantages, Prussia achieves what can be described as the first blitzkrieg (lightning war). Troops are transported to various points on a front of about 270 miles along the northern border of Bohemia (part of the Austrian empire).

Entering Bohemia at several different places, the invading forces form into a single army to confront the Austrians in a major battle at the village of Sadowa, near Königgrätz, on July 3. The result is inconclusive, but the Prussians are able to push on south to the outskirts of Vienna - where an armistice is agreed on July 22.

Meanwhile other Prussian armies have been winning victories against Hanover in the west and against Bavaria (and other smaller states loyal to the German Confederation) in the southwest. An armistice has been agreed on all fronts by the end of July, bringing the hostilities to an end within seven weeks.

With the treaty signed in Prague, on August 23, Bismarck demonstrates conclusively that the leadership of the German world, exercised for four centuries by Habsburg Austria, has now passed to Hohenzollern Prussia.

The specific point at issue is resolved by Austria ceding all rights in Schleswig-Holstein to Prussia. More important is the article in the treaty where Austria consents to a 'new organization of Germany' from which Austria will be excluded. This is all that Bismarck needs. His king, William I, is eager to annexe part of Austria. But Bismarck prefers a humiliated but intact Austrian empire on his southeastern flank. On this point Bismarck prevails. Prussian policy is clearly to be his policy.

North German Federation: 1867-71

With a free hand now in Germany, Bismarck immediately annexes two Protestant states in west Germany which have opposed him in the recent war - Hanover and Hesse-Kassel. They are a particularly welcome acquisition because they bridge the previous gap between the main Prussian kingdom and Prussian territories on the Rhine.

All other German states north of the river Main are now merged under Prussian leadership in a new North German Federation. This differs little in organization from the previous German Confederation led by Austria, except that it is a more coherent Protestant bloc.

The three Catholic states south of the Main (Baden, Württemberg, Bavaria) are now a separate group, recognized as having 'an internationally independent existence' - a condition agreed by Bismarck with the Catholic emperors west and east, in France and Austria. However these Catholic regions retain a strong economic link with north Germany. A continuation of the old Prussian Zollverein is agreed in 1867, again incorporating all the German-speaking regions except Austria.

With Austria reduced to impotence by defeat in the Seven Weeks' War, the only other neighbour inclined to challenge Prussia's inexorable growth is France. The clash perhaps comes sooner than France might wish. But Bismarck is ready.

Franco-Prussian War: 1870-71

Ever since Prussia's rapid success in the Seven Weeks' War of 1866, and the resulting consolidation of Prussian territory on the Rhine, there has been alarm and resentment in France at the growth of this ambitious neighbour. It is dramatically increased in 1870 when news leaks on July 3 that a prince of the Prussian Hohenzollern family has been offered, and has accepted, the vacant throne of Spain.

Having fought so often in the past against being surrounded to south and east by the Habsburg dynasty, there is public outcry in France at the prospect of the same trick now being pulled off by the Hohenzollern. In an escalating crisis, the Prussian king William I withdraws his relation's candidacy on July 12.

The matter might have rested there, but for a diplomatic blunder on the French side. The French ambassador, in an audience with William I at Ems on July 13, demands an assurance (amounting to a slur on the king's good faith) that the candidacy will never be renewed. William refuses to give this assurance. He then sends a telegram to Bismarck describing, in neutral terms, the audience and its outcome.

Bismarck, irritated at the collapse of his Spanish policy, shortens the telegram before publication in such a way as to imply that the Prussian king has treated the French ambassador with disdain. Public opinion in France, already inflamed, now explodes. The French government declares war on Prussia on July 19.

France suffers as rapidly and as conclusively at Prussia's hands as Austria did four years previously. Again the significant period of warfare lasts less than seven weeks. In early encounters near Metz the French almost hold their own against the Prussians, but by August 31 a large French army is surrounded near Sedan.

During September 1 the French cavalry, charging desperately to break out of the encirclement, suffer heavy casualties from the Prussian artillery. On the following day the French surrender. After losses in the battle of 38,000 men (killed, wounded or missing), another 83,000 now lay down their arms and become prisoners of the Germans. Among them is the French emperor himself, Napoleon III.

The events at Sedan bring to an end one empire, in France, and hasten the creation of another, in Germany. But they do not immediately end the war.

When the news of Sedan reaches Paris, a government of national defence is rapidly formed. Its first action, on September 4, is to depose Napoleon III and declare a republic. But there is nothing now to stop the German army on its march towards Paris. The siege begins on September 19. The only chance of relieving the city is to raise new armies in the provinces. And here aeronautics play their first significant role in warfare.

On October 7 a balloon rises from Paris (historic city of the balloon). It floats above the Germany army and lands far beyond their lines. It carries Léon Gambetta, minister of the interior in the new republican government. Two days later he reaches Tours and begins to orchestrate a campaign of guerrilla warfare which severely disrupts the smooth Prussian military operation.

But it can only delay the eventual capitulation. Early in 1871, on January 23, delegates from Paris pass through the German lines to Versailles to agree an armistice. They find the Prussians in an excited mood. Just five days previously, in Louis XIV's famous hall of mirrors in the palace of Versailles, the Prussian king has been proclaimed emperor of a united Germany.

The German empire: 1871

The creation of the German empire, long a cherished intention of Bismarck's, is much eased by the Franco-Prussian war. When France declares war in 1870, the three independent south German states (Baden, Württemberg and Bavaria) place their armies under the command of the Prussian king, William I, in what is seen as an essentially German cause.

After the victory at Sedan, talks are held to discuss possible German unification. By November terms are agreed. Minor concessions to Bavaria are devised to give the impression of semi-independence, but essentially this is to be a single state under Prussian leadership.

William I is extremely reluctant to accept the title of emperor, but Bismarck contrives to persuade him. His proclamation in the Hall of Mirrors at Versailles (the symbol of French power and triumphalism) is sweet revenge for the humiliation of Prussia at Napoleon's hands in the early years of the century. In the treaty of Frankfurt France cedes Alsace and most of Lorraine to the new Germany, pays a masssive indemnity of 5000 million francs and suffers German occupation in part of France until the money is delivered (a precise echo of France's terms in 1807).

As an added twist of the knife, Bismarck imposes a victory march of Prussian troops through the streets of Paris.

The reconstitution of the ancient German Reich, in a modern, compact, national form, brings back the Reichstag as a parliament. Meeting in Berlin, with delegates elected from all over the new nation, it is only a legislative body with little control over the executive.

Now more firmly than ever, the executive is Bismarck himself - the first imperial chancellor. His German empire, like its medieval prototype, consists of clearly separate constituent states (4 kingdoms, 5 grand duchies, 13 duchies and principalities, and the free cities of Hamburg, Lübeck and Bremen). But it is at last a nation, federal in kind but with strong central control. The story of Prussia becomes that of Germany.